This application claims the priority of German patent document 103 00 773.3, filed Jan. 11, 2003, the disclosure of which is expressly incorporated by reference herein.
The invention relates to an exhaust system of a multi-cylinder internal combustion engine.
U.S. Pat. No. 5,351,481 discloses an exhaust system of a multi-cylinder internal combustion engine, in which the exhaust gas from two cylinder groups of the internal combustion engine is received by a respective exhaust-gas line that terminates with its open end in an exhaust-gas expansion chamber. An exhaust-gas outlet line leading out of the exhaust-gas expansion chamber terminates in each case at a short distance from the open end of each of the exhaust-gas lines. This exhaust system is intended to achieve both sound insulation and an improvement in performance of the internal combustion engine.
One object of the invention is to provide an exhaust system of a multi-cylinder internal combustion engine, which permits improved noise emission and power output of the internal combustion engine.
This and other objects and advantages are achieved by the exhaust system according to the invention, in which the first and second exhaust-gas lines are lead into an at least partially perforated exhaust-gas mixing chamber. The exhaust-gas mixing chamber is coupled in gas flow communication with an exhaust gas expansion chamber, so that exhaust gas can expand out of the exhaust-gas mixing chamber into the exhaust-gas expansion chamber, via the perforation of the exhaust-gas mixing chamber.
The cylinder groups to which the exhaust-gas lines are connected in each case may be formed by any desired cylinders of a multi-cylinder internal combustion engine. However, the exhaust system according to the invention is suitable, in particular, for an internal combustion engine designed as a V-engine with two cylinder banks. In this case, the cylinder groups are formed by the two cylinder banks. Preferably, each of the exhaust-gas lines is connected via an associated exhaust-gas manifold to one cylinder group and receives the exhaust gas from the cylinder group. The exhaust-gas streams of the cylinder groups are discharged separately from the exhaust-gas lines and are combined in the exhaust-gas mixing chamber.
The exhaust-gas expansion chamber is in this case designed as a housing which is outwardly substantially gas-tight. Together with the exhaust-gas mixing chamber, it forms an arrangement in which the exhaust gases emerging from the exhaust-gas mixing chamber via the perforation can be received completely.
The exhaust-gas mixing chamber may be designed as a line element of any desired form, in which the exhaust-gas streams are combined and the outer surface area of which has a perforation preferably along a defined portion. The perforation may be designed as an orifice of any desired form, but it is preferably formed by a multiplicity of identical orifices arranged uniformly on the portion and is implemented, for example, by round orifices with a diameter of about 5 mm. Preferably, the first and the second exhaust-gas line are closed off by means of the exhaust-gas mixing chamber, so that the exhaust-gas mixing chamber forms, as it were, a short circuit with respect to the first and the second exhaust-gas line.
The exhaust-gas mixing chamber is flow-connected to the exhaust-gas expansion chamber via the perforation. The exhaust-gas streams conducted out of the exhaust-gas lines into the exhaust-gas mixing chamber meet one another in the exhaust-gas mixing chamber, are intermixed and can flow over into the exhaust-gas expansion chamber via the perforation acting as overflow orifices. As a result, noise emission is reduced.
By means of special structural embodiments, the acoustic pattern can be influenced in a controlled manner, preferably in the form of a sound-insulating action. The discharge of the exhaust gases from the exhaust-gas expansion chamber takes place via the exhaust-gas outlet line leading out of the exhaust-gas expansion chamber.
The exhaust-gas outlet line is designed as a pipeline which, open on the end face, issues into the exhaust-gas expansion chamber. Preferably, the exhaust-gas outlet line is formed by two separate pipelines. These are preferably led out of the exhaust-gas expansion chamber next to one another.
The exhaust-gas mixing chamber according to the invention acts, as it were, as a short circuit with respect to the exhaust-gas streams delivered via the first and the second exhaust-gas line. The length of the exhaust-gas lines and the perforated portion of the exhaust-gas mixing chamber are preferably defined in such a way that an interference of the gas oscillations occurs when the two exhaust-gas streams meet in the exhaust-gas mixing chamber. This helps to optimize the torque delivered by the internal combustion engine, while at the same time achieving improved noise emission, preferably sound insulation. In particular, due to the suitably defined flow-active distance of the exhaust-gas mixing chamber from the outlet valve of the engine, a gas-dynamic benefit having an effect on the engine torque can be achieved, since pressure waves and suction waves in the exhaust-gas lines can advantageously interact with one another. These gas-dynamic benefits can be enhanced by a suitable selection of valve control times. Moreover, the design according to the invention achieves good intermixing of the exhaust-gas streams meeting one another in the exhaust-gas mixing chamber, favorably affecting the acoustics, particularly with regard to the engine secondary orders, even in the case of a limited construction space.
In one embodiment of the invention, the exhaust-gas mixing chamber is arranged directly adjacent to the exhaust-gas expansion chamber, so that a direct overflow and expansion of exhaust gas via the perforation of the exhaust-gas mixing chamber into the exhaust-gas expansion chamber is possible.
Preferably, the exhaust-gas mixing chamber and the exhaust-gas expansion chamber are designed to rest against one another, and the exhaust-gas expansion chamber has, in the region of contact, one or more orifices which overlap the perforation of the exhaust-gas mixing chamber. The exhaust-gas mixing chamber and the exhaust-gas expansion chamber may, however, also have a perforated common partition, via which the overflow and, if appropriate, expansion of exhaust gas can take place.
In a further embodiment of the invention, the exhaust-gas mixing chamber is arranged in the exhaust-gas expansion chamber, which achieves a compact and space-saving arrangement. Preferably, the exhaust-gas lines issuing into the exhaust-gas mixing chamber lead through the exhaust-gas expansion chamber wall and the exhaust-gas streams are combined in the exhaust-gas mixing chamber. In the region where the exhaust gases are combined, therefore, the exhaust system has a double casing, so that especially good sound insulation can be achieved.
In a further embodiment of the invention, the exhaust-gas mixing chamber is designed as a connecting line by which the first exhaust-gas line and the second exhaust-gas line are combined. Preferably, the connecting line is designed as a simple pipeline which acts as a short-circuit line with respect to the first and the second exhaust-gas line. This design permits a structurally simple and effective control of the exhaust-gas acoustics.
In a further embodiment of the invention, the exhaust-gas mixing chamber has a perforation made uniformly all-round. If a pipeline is arranged as an exhaust-gas mixing chamber in the exhaust-gas expansion chamber, the pipeline has one or more portions perforated uniformly all-round. It is thus possible to have a radially uniform overflow of exhaust gas into the exhaust-gas expansion chamber, and to influence noise emission positively.
In a further embodiment of the invention, the exhaust-gas outlet line has a portion branching off from the first exhaust-gas line and/or from the second exhaust-gas line upstream of the exhaust-gas mixing chamber. The portions of the exhaust-gas outlet line which branch off from the exhaust-gas lines are combined, outside the exhaust-gas expansion chamber, with the portions of the exhaust-gas outlet line which lead out of the exhaust-gas expansion chamber. In a particularly preferred embodiment, the exhaust-gas outlet line is of double-flow design, and each of the flows has a branch-off from an exhaust-gas line, with the branch-off being arranged within the exhaust-gas expansion chamber. In this case, the exhaust-gas mixing chamber is also arranged in the exhaust-gas expansion chamber. In addition, each of the exhaust-gas outlet flows has a portion led into the exhaust-gas expansion chamber, with an open end for the discharge of exhaust gas from the exhaust-gas expansion chamber. The portion branching off from the exhaust-gas line is combined, outside the exhaust-gas expansion chamber, with the portion leading out of the exhaust-gas expansion chamber. This arrangement helps to achieve an especially effective control of the acoustics, particularly in terms of the engine secondary orders.
In a further embodiment of the invention, the first exhaust-gas line and/or the second exhaust-gas line, the exhaust-gas outlet line has a perforated portion led through a housing outside the exhaust-gas expansion chamber. An additional expansion of the exhaust gas due to emergence from the exhaust-gas line can occur in this housing. This embodiment therefore serves mainly for further sound insulation.
Preferably, both the first and the second exhaust-gas line have such a perforated line portion in a specific housing assigned to them in each case. The respective housings may be separate from one another. Preferably, however, they are designed to lie next to one another with a common partition. In a particularly preferred design, the exhaust-gas mixing chamber is arranged within the exhaust-gas expansion chamber and the housing or housings is or are contiguous, on the end face, to the exhaust-gas expansion chamber, thus resulting in a common partition with the exhaust-gas expansion chamber. This makes it possible to have a material-saving and compact arrangement.
In a further embodiment of the invention, means are provided for closing a predeterminable part of the perforation of the exhaust-gas mixing chamber. When the exhaust-gas mixing chamber is of tubular design, the closing means may be, for example, a sleeve which is displaceable so as to rest against the wall on the inside or on the outside. As a result of such displacement, a variable and predeterminable part of the perforation can be closed or opened, as required. Preferably, closing is executed in such a way that a perforation part predetermined as a function of the operating state of the internal combustion engine can be closed or opened.
The invention advantageously makes it possible to influence the noise and to influence the torque as a function of the driving state of the associated vehicle.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.